My dog-human communication students recently discussed a study on how well people interpret dog body language. The study, published in 2009, compared the descriptions of dog professionals, dog owners, and people with no dog experience. They all watched the same nine videos that showed a range of behaviors, most interestingly aggression and actual play.

The study’s authors wanted to know whether the amount of dog experience a person had improved his or her skills at reading dogs’ body language. They showed the video clips to observers from four different groups: veterinarians, professional trainers, dog owners, and people with no dog experience. The dog professionals and owners had at least two years of hands-on dog experience.

After watching each clip, observers were to identify the predominant behavior, choosing from a list of eight adjectives. They were then asked to justify their choice: What about the dog’s body language suggests this behavior?

How’d they do?

Not well. Professional trainers (other than the ones participating in the study) and behaviorists have their work cut out for them.

Surprisingly, the dog professionals did no better than the people with no dog experience at identifying the dogs’ body language.

• The scariest result was that a third of the observers saw aggressive behavior as playful.
• A sad result was that 43 percent saw actual play as aggression.

Too many people can’t tell when a dog is playing and when the dog is being (or working up to becoming) aggressive. That’s often why people get bitten.

The observers’ descriptions of the body language they relied on to identify behavior are revealing. For example:

• Most descriptions focused on tail movement, mouthing or vocalizing, and large, whole-body movements.
• Nearly all tail movement was described as “wagging” and it was always identified as playful.
• Nearly all barking was seen as aggressive and growling as defensive.
• The only clip where a dog’s teeth could be seen was the active play video, but two-thirds of the observers who mentioned it saw it as aggression.

That’s another reason behind dog bites, especially the ones where people say “it came out of nowhere.” They look only at big, dramatic body movement and assume that barking or tail movement has only one purpose. They miss or misinterpret the more subtle body language and vocalizations.

If our dogs ever interact with other dogs, with children, even with unfamiliar adults, we need to be able to intervene if the dog is stressed or scared, remove the dog if he or another dog is showing stress, aggression, or fear, and generally pay attention to how our dogs react to different situations. This enables us to keep — and the people and dogs who interact with them — safe.

To do this, we have to look at the whole dog. A wagging tail might mean the dog is happy or wants to play — or it could indicate that he is stressed or unsure of the situation. Raised hackles might be defensive or aggressive — or could simply indicate arousal, which is more likely the case in an actively playing dog.

Not knowing this and not noticing the more subtle movements — a raised lip, ears pulled back, a stress smile — is how people miss the early signs that a situation is overwhelming or frightening to a dog, that the dog is losing patience or getting close to a literal “snapping point.”

When it’s our own dogs, the more often we watch and notice, the better we’ll get at putting together a “big picture” understanding of our dogs’ body language and of the messages they are sending us.

(Oh — those dogs in the photo? Playing. How can you tell? There are many cues: Hackles are not raised, eyes are soft, ears are loose and not pinned back, tails are low and not stiff, both dogs are showing similar energy (one is not going after the other), lips are not pulled back from teeth.)